1. Field of Invention
The present invention relates to a method of synthesizing ethylene glycol, and more particularly to tungsten carbide catalysts and the preparation, as well as the application in the reaction of preparing ethylene glycol by hydrogenating degradation of cellulose.
2. Description of Related Arts
Ethylene glycol is an important liquid energy fuel and very important feed for polyester synthesis. For example, Ethylene glycol is used for synthesis of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). It is also used as antifreeze, lubricants, plasticizers, surface active agent, etc. Thus it is an organic chemical material with wide applications. In recent years, its demand maintains a growth rate of 6˜7% world widely. China has a huge consumption of ethylene glycol. In 2005, the market demand is 5 million tons, accounting for 25% of the world's total production, nearly 80% of which had to be imported. Ethylene glycol is one of China's “Ten key imported products”.
Currently, industrial production of ethylene glycol is mainly depending on petroleum as the raw material. The ethylene glycol is produced via ethylene oxidation to form the epoxyethane, followed with hydration to form the final product. [Reference 1: Shen, Ju-hua, Overview of ethylene glycol production, Chemical Technology Market, 2003, 26, (6), 12-15. Reference 2: Process for preparing ethanediol by catalyzing epoxyethane hydration, Patent No. CN1463960-A; CN1204103-C]. This method consumes non-renewable petroleum resources. Also the producing process includes steps of selective oxidation and epoxidation, which confronts many technique difficulties, such as low efficiency, large amount of by-products, high material consumption and pollution.
Using biomass to prepare ethylene glycol can reduce human's dependence on the fossil energy resources, because it is environment friendly and contributing to the sustainable development of the world. Currently the research of biomass conversion to ethylene glycol mostly focuses on the raw materials such as starch, glucose, sucrose, and sugar alcohols. [Reference 3: Process for the preparation of lower polyhydric alcohols, U.S. Pat. No. 5,107,018. Reference 4: Preparation of lower polyhydric alcohols, U.S. Pat. No. 5,210,335.]. These raw materials themselves are food for mankind, so that using them to prepare chemicals will cause the conflict between survival and development of the mankind. In contrast, cellulose is the largest renewable biomass with rich resources but indigestible for human being, such as agricultural production, remaining straw and forestry wastes, so that it is abundant and cheap. The use of cellulose to prepare ethylene glycol enables a new synthetic method to obtain high value products with low cost, meanwhile this will not affect the food supply. In addition, cellulose is formed by polycondensation of glucose units via glycosidic bonds, containing a large number of hydroxyl. In the process of cellulose conversion to ethylene glycol, the hydroxyl is fully retained, so that this transformation process has very high atom economy. Thus, the conversion of cellulose to ethylene glycol has a number of significant advantages unmatched by many other production methods.
However, because the structure of cellulose is much more stable than other biomass, it is a considerable challenge to convert cellulose into small molecule polyols with high efficiently and high selectivity. According to the survey of current literature, there is no report of any works for the cellulose conversion into ethylene glycol with high efficiency and high selectivity with tungsten carbide catalysts.